New Comp Sluggish

Hey guys, first time on this forum. Trying to find some advice to fix my new PC.

Just bought and assembled new PC (specs in signature). My system will frequently 'lock' up or 'freeze'. I've noted that the HDD light on the front of the case is on constantly when this occurs. I've gone into the Performance Monitor and the 'Avg Disk Que Length' spikes to 100% when the 'locking' up happens.

I've switched video cards and HDD's with the same exact result. I am using XP Pro SP2. I'm kind of at a loss of what to do.

I've set msconfig to only start necessary items so I don't believe it is a process slowing me down.

After putting in the new HDD and new vid card it worked fine for hours. Ran SuperPi with no problems. Temps are no higher than 52C at peak load.

I have not changed anything in the bios other than the boot order(HDD first).

New PC? Then new hard drive? Is the computer one you built or one you purchased which was shipped from some long distance?
Any chance a cable is loose? Or memory? Or other hardware?
Does the computer have a floppy drive which you could use to go back to fundamental startups with a power supply, floppy drive, boot floppy, and one memory module, connected to the video graphics socket?
Lock ups are commonly caused by memory modules, video graphics cards, cpu fans, power supply defects, loose or defective cables... hard to narrow down...
So start with a plan, and keep notes... Create the most simple configuration you can, then switch out parts, try again... by have a system...
Oh, and aahhh... don't try to fix it while you are tired or stressed.

Can it be anything other than a bad motherboard, assuming you have performed a full reformat and reinstall of WXPP?
First, I would download and run the drive fitness software for your model and serial number of hard drive... just to rule that drive out, then be sure you have a couple of full scans for antivirus and antispyware while in Safe Mode. Then, I would get on the phone or online with the tech support people of the motherboard manufacturer.
We see a surprising number of failing new motherboards of a number of brands... so it is not all that unusual to have the problems you describe.